Page 137 - Demo

Absence of cognitive bias to flanges in orang-utans1356reports published by Bornean orang-utan reintroduction programs. These were supplemented with portrait pictures taken from semi-wild orang-utans and pictures of zoo-housed orang-utans within the orang-utan EEP. All of the stimuli depict front-facing Bornean orang-utan males. We cropped their faces using GIMP (v2.10.32) and pasted the cropped faces on a light-grey background (#808080), resulting in stimuli with an 18:13 aspect ratio. From both the flanged and the unflanged stimuli, we randomly selected four stimuli (eight in total) to use as stimuli in the forced-trial phase of the experiment. The remaining 48 stimuli of each category were randomly distributed across three sessions. ProcedureDot-probe taskThe procedure for the dot-probe task was almost identical to the one described in Laméris et al. (2022). A trial consisted of five phases (Figure 1). First, a 200x200-pixel black dot appeared on a random position on the screen and had to be clicked. We added this step to avoid anticipatory responses. Second, the dot appeared in the lower, middle part of the screen. Touching this dot activated presentation of two stimuli (500x375 px) that were vertically positioned in the middle of the screen, and horizontally equidistant from the center of the screen (20% vs. 80%). After 300ms, the stimuli disappeared and only one of the stimuli was replaced by a dot (the probe) that remained on the screen until touched by the subject. Touching the dot resulted in a reward (sunflower seed). After an intertrial interval of 3s, a new trial started. The background of screen was white during all steps of the trial.Trials were presented in randomized order. For the flange size dot-probe, each individual participated in 6 sessions consisting of 24 trials. For the symmetry dotprobe, each individual participated in 8 sessions consisting of 20 trials. All stimuli were presented twice across all sessions: once as probed stimulus (replaced by dot), once as distractor stimulus (not replaced by dot). At the end of the test sessions, we created extra sessions per subject to repeat outlier trials (see Statistical analysis). All data were collected between February and December 2020, with a test stop between March and July 2020 due to COVID-19.Two of the three participating individuals were already trained on the task for a previous study (Laméris et al., 2022). They received a few training sessions to check whether they still executed the task correctly, which was the case. For the other individuals, we employed a similar training procedure. Only one of the Tom Roth.indd 135 08-01-2024 10:41